1) Field of the Invention
The present invention relates to a library system in which a virtual library apparatus is interposed between a library apparatus and a data processing apparatus. Particularly, the present invention relates to a technique for restoring contents of a cache which is provided in the virtual library apparatus, and holds data read out from a physical volume in the library apparatus as a logical volume in order that the data processing apparatus has an access to the data to process the same.
2) Description of the Related Art
FIG. 9 is a schematic diagram showing a structure of a known library system 100. The library system 100 shown in FIG. 9 comprises a library apparatus 20 and a data processing apparatus (host) 30.
The library apparatus 20 comprises an accommodating shelf 22 accommodating a plurality (here, 64) of recording media (for example, magnetic tapes, magneto-optic disks, optical disks) 21, a plurality (here, six) of drive units 23 for processing the recording media 21, and a transporting mechanism (accessor) 24 for transporting the recording media 21 between the accommodating shelf 22 and the drive units 23.
The data processing apparatus 30 processes data recorded on the recording media 21 in the library apparatus 20. The data processing apparatus 30 controls the transporting mechanism 24 to transport a recording medium 21 from the accommodating shelf 22 to the drive unit 23, and controls a processing unit of the drive unit 23 to perform a process (Read/Write) on the recording medium 21. When the process is completed, the data processing apparatus 30 controls the transporting mechanism 24 to transport the recording medium 21 from the drive unit 23 to the accommodating shelf 22.
With improvement of the technique, the recording capacity of the recording medium 21 is increased, and the processing performance (Read/Write performance and the like) of the drive unit 23 is improved, in these years.
In the library system 100 shown in FIG. 9, the data processing apparatus 30 using the recording media 21 and the drive units 23 is fabricated on the assumption that conventional recording media having small capacity and drive units having low processing performance are used in order to keep the compatibility with conventional software resources/hardware resources. Thus, the data processing apparatus 30 cannot sufficiently use performances of recent recording media having large capacity and drive units having high processing performance.
To cope with this drawback, there has been proposed a library system in which a virtual library apparatus configuring virtual recording media and virtual drive units is interposed between the data processing apparatus and the library apparatus, its substance (that is, the library apparatus) is configured with the latest recording media and drive units, and the data processing apparatus has an access similar to an access to a conventional recording medium and drive unit, thereby accessing to the latest recording media and drive unit (refer to Patent Document 1 below, for example).
FIG. 10 is a schematic diagram showing a structure of a library system 100′ having a known virtual library apparatus 40. In FIG. 10, like reference characters designate like or corresponding parts in FIG. 9, detailed descriptions of which are thus omitted. As shown in FIG. 10, the library system 100′ has a virtual library apparatus 40 between the library apparatus 20 and the data processing apparatus 30, along with the library apparatus 20 and the data processing apparatus 30. The virtual library apparatus 40 has a logical layer (front end) 41, a physical layer (back end) 42, a control unit 43 and a cache 44.
The logical layer 41 controls the inputs/outputs to/from the data processing apparatus 30. The logical layer 41 emulates the conventional recording media, drive units and transporting mechanism assumed by the data processing apparatus 30. In FIG. 10, the drive units and the transporting mechanism emulated by the logical layer 41 are denoted by a reference character 45. Hereinafter, the drive unit configured by emulating by the logical layer 41 will be referred to as a logical drive.
When the data processing apparatus 30 has an access, the physical layer 42 reads out data to be accessed from a recording medium (hereinafter referred to as a physical volume) 21 using a drive unit (hereinafter referred to as a physical drive) 23 of the library apparatus 20. When the data processing apparatus 30 completes (unloads) the process, the physical layer 42 records the user data (logical volume) undergone the process (Read/Write) by the data processing apparatus 30 on the physical volume 21 using a physical drive 23.
The control unit 43 controls the logical layer 41 and the physical layer 42.
The cache 44 holds, as a logical volume, data read out from a physical volume 21 by the physical layer 42 in order that the data processing apparatus 30 processes the data. Even when the logical volume is recorded on the physical volume 21 by the physical layer 42 after the process by the data processing apparatus 30, the cache 44 keeps holding the logical volume as it is.
When a capacity of a new logical volume cannot be secured on the cache 44 in response to a request to mount the new logical volume from the data processing apparatus 30, the oldest logical volumes on the cache 44 are deleted in the order of the capacity until the necessary capacity is secured.
The cache 44 is comprised of, for example, a RAID (Redundant Arrays of Inexpensive Disk).
When the data processing apparatus 30 makes a request to mount a logical volume in the library system 100′, a process (1) or (2) below is performed:
(1) Confirming whether or not a logical volume requested by the data processing apparatus 30 is present on the cache 44. When the logical volume is present on the cache 44, “READY” is immediately reported on a designated logical drive.
(2) Confirming whether or not a logical volume requested by the data processing apparatus 30 is present on the cache 44. When the logical volume is not present on the cache 44, confirming whether or not there is a free capacity sufficient to load the logical volume into the cache 44. When the free capacity is not sufficient, deleting the oldest logical volume on the cache 44 to secure the free capacity. The control unit 43 controls the physical layer 42, whereby the physical layer 42 mounts a physical volume 21 retaining the logical volume requested by the data processing apparatus 30 onto a physical drive 23, reads the logical volume, loads the logical volume into the cache 44, and reports of “READY” on the designated logical drive.
In the library system 100′, when a logical volume requested by the data processing apparatus 30 is present on the cache 44 [that is, when the process (1) is performed], it is possible to immediately (within one second) make the “READY” response in response to the mount request from the data processing apparatus 30.
When the logical volume requested by the data processing apparatus 30 is not present on the cache 44 [that is, the above process (2) is performed], it is necessary to read out the logical volume from the physical volume 21. For this, there is a case where the “READY” response cannot be immediately made in response to the mount request from the data processing apparatus 30, and it takes one minute or more to make the “READY” response. In the library system 100′, a logical volume frequently accessed from the data processing apparatus 30 is mostly present on the cache 44, thus it is rare that the logical volume has to be read out from the physical volume 21.
In the library system 100′ shown in FIG. 10, when the cache 44 is replaced with a new cache due to, for example, a fault or a change in the capacity, there is no case where data to be held is deleted because logical volumes held in the cache 44 are also held in the physical volumes 21.
However, immediately after the cache 44 is replaced with another new cache, it is necessary to read a requested logical volume from the physical volume 21 onto the new cache each time the data processing apparatus 30 makes a request to mount the logical volume. For this, the response to the data processing apparatus 30 is noticeably degraded, and the response speed to the processing request from the data processing apparatus 30 is decreased as compared with before the replacement of the cache.    [Patent Document 1] Japanese Unexamined Patent Application Publication No. HEI 11-272426